In the cable making art there are generally two types of insulation and/or jacket materials used in the fabrication of electrical wire and cable; i.e., thermosetting materials and thermoplastic materials. The application of thermoset materials as the insulation or jacket of an electrical wire or cable requires use of vulcanization (curing) apparatus to cause the thermosetting reaction to occur. The most widely accepted technique of manufacturing extruded vulcanized type cables is to pass the conductor through a series of extruder heads and apply concentrically the plastic compounds. After application of the plastic compounds, the cables are usually vulcanized (cured under pressure) in a saturated steam environment followed by cooling under pressure. In such a steam curing process, the insulated conductor is moved through the vulcanizer and exposed to pressurized (typically 250 psi) saturated steam followed by cooling under pressurized water (typically 250 psi). The thermosetting compound contains curing agents which are activated at the high temperatures found within the vulcanizer with the speed of the vulcanization reaction depending on the temperature within the vulcanizer (for 250 psi steam, approximately 210.degree. C.).
The steam curing process has been used in horizontal, vertical, slant and catenary installations. Long length curing pipes have been demonstrated to be preferred by those practicing the art of steam curing cables; this is so because the polyethylene and ethylenepropylene rubber insulations commonly used characteristically have high thermal resistances and therefore heavily insulated cables of the type used for high voltage operation take a long time to cure. Alternatively, higher temperature and pressure inert gases may be used to cure the insulation, and may be coupled with a dry cooling process to cool the cured insulation.
Strict manufacturing tolerances require a minimum thickness of plastic, typically at least several thousandths of an inch. Manufacturing process and cost controls, however, dictate that maximum extra thickness be limited in order to facilitate production and reduce material costs. Visual and/or optical access to the moving wire is thus necessitated for measurement. However, the fragile and delicate uncured plastic cannot be touched, and it is contained within an elongated pressurized tube, filled with heated steam or pressurized inert gas.
Various styles of sight gauge glass configurations have been used by experts in the industry, all of which experience shows are either fragile, expensive, short-lived, and/or difficult to install and maintain. A particularly difficult problem associated with the prior art sight glasses used in vulcanizing lines is their predilection for becoming dirty and/or fogged on the inaccessible inside thereof, requiring shut down, disassembly and very costly cleaning. The present invention is directed to solving these and other problems associated with the prior art.